Endoscopes are widely used for a variety of medical procedures. To improve their performance, endoscopes have been optimized in various ways to best accomplish their purpose. Examples of specialized endoscopes include angioscopes, colonoscopes, bronchoscopes, and arthroscopes.
One of the medical procedures that may be performed using an endoscope is obtaining a biopsy sample. FIG. 1 shows a conventional endoscope assembly 10 used for obtaining a biopsy sample. The endoscope assembly 10 includes an endoscope 20 having an elongated insertion tube 22. The insertion tube 22 may be rigid, partially flexible, or entirely flexible The insertion tube 22 includes a distal portion 24 that may be inserted into a body cavity of a patient (not shown), and a working end 26.
The endoscope 20 includes a headpiece 28 that remains external to the patient during a medical procedure. In the embodiment shown in FIG. 1, the headpiece 28 includes an eyepiece 30 for viewing the scene through a viewing lens 31 at the working end 26 of the insertion tube 22, a pair of articulation control knobs 32 for manipulating the position of the distal portion 24 of the insertion tube 22, and a pair of fluid control actuators 34 for controlling the flow of fluids through tubes 36 to (or from) the working end 26. Endoscopes 20 of the type generally shown in FIG. 1 are described more fully, for example, in U.S. Pat. No. 5,931,833 issued to Silverstein, U.S. Pat. No. 5,483,951 issued to Frassica and Ailinger, and U.S. Pat. No. 4,714,075 issued to Krauter and Vivenzio, which patents are incorporated herein by reference. Representative commercially-available endoscopes include, for example, video or fiberoptically-equipped sigmoidoscopes, bronchoscopes, nasopharyngo-laryngoscopes, colonoseopes, and gastroscopes.
As further shown in FIG. 1, the endoscope assembly 10 includes a sheath 40 that encapsulates the insertion tube 22 to prevent at least part of the insertion tube 22 from being soiled during the medical procedure. The sheath 40 may be flexible to allow unrestricted bending of the flexible portion of the insertion tube 22, or may be relatively rigid. In the depicted embodiment, the sheath 40 includes an enlarged fitting portion 42 that fits over an engagement portion 44 of the headpiece 28, and a working channel 46 having a proximal end 48 that projects outwardly from the sheath 40 proximate the headpiece 28.
FIG. 2 is an enlarged isometric view of the working end 26 of the endoscope assembly 10 of FIG. 1. As shown in FIG. 2, the sheath 40 surrounds the insertion tube 22 of the endoscope 20, and the working channel 46 extends along an outer surface of the insertion tube 22. The working channel 46 terminates in an open distal end 49 at the working end 26 of the insertion tube 22. A medical instrument 50, including a biopsy sampling device 52, extends through the working channel 46 (see FIG. 1) and projects from the open distal end 49 of the working channel 46. Sheaths of the type shown in FIGS. 1 and 2 are described more fully, for example, in U.S. Pat. No. 5,025,778 issued to Silverstein et al., U.S. Pat. No. 5,483,951 issued to Frassica et al., and U.S. Pat. No. 5,827,177 issued to Oneda et al.
During a medical procedure, the medical instrument 50 is inserted into the proximal end 48 of the working channel 46 and slid through the working channel 46 until the biopsy sampling device 52 emerges from the open distal end 49 at the working end 26. Through the eyepiece 30, the physician observes the biopsy sampling device 52 through the viewing lens 31 and manipulates the medical instrument 50 into the desired position and collects the desired sample. After a biopsy sample is obtained, the biopsy sampling device 52 containing the biopsy sample may be withdrawn through the working channel 46, or alternately, the entire insertion tube 22 may be withdrawn from the patient's body with the biopsy sampling device 52 remaining in position near the working end 26.
Although desirable results have been achieved using the conventional devices described above, some drawbacks do exist. For example, during a medical procedure, the flexible insertion tube 22 is generally manipulated into various bending positions using the articulation control knobs 32. It is therefore desirable for such endoscope assemblies that the sheath 40, including the working channel 46, be fabricated of a flexible material to allow for bending and articulation of the insertion tube 22. Furthermore, it may be desirable to axially stretch the sheath and working channel when positioned on the insertion tube 22 to maintain a tight engagement between an enclosed, transparent end cap of the sheath and the viewing lens 31 of the insertion tube 22, as described more fully, for example, in co-pending, commonly-owned U.S. patent application Ser. No. 09/235,355.
For these reasons, sheaths are commonly constructed of a flexible elastomeric material. A variety of known flexible materials are used for this purpose. Generally speaking, however, such known flexible materials have high coefficients of friction that inhibit the movement of medical instruments through the working channel. In some situations, such as at a sharp bending corner along the insertion tube, the medical instrument may be unable to progress through the working channel, or may even become stuck, necessitating the removal of the insertion tube.
To reduce the coefficient of friction of the internal surface of the working channel, a variety of techniques have been employed. One approach has been to line the working channel with a relatively-hard corrugated material having a low coefficient of friction, such as materials sold under the trademark TEFLON®. Because the relatively-hard corrugated material has a lower coefficient of friction than the flexible material of the working channel, the medical instrument moves more easily through the working channel, and the corrugations allow the necessary bending and axial stretching of the working channel. Unfortunately, the lining of relatively-hard corrugated material greatly increases the thickness of the wall of the working channel, and thus, the overall diameter of the endoscope assembly. Thus, the sheath having a working channel lined with a relatively-hard corrugated material may increase the discomfort or trauma experienced by the patient, or may not be practical for some medical procedures due to size constraints within the patient's body. Also, the cost of manufacturing the working channel lined with the relatively-hard corrugated material is undesirably high. Finally, although the corrugated channel does stretch axially, it does not do so easily.